Biomedical Engineering Reference
In-Depth Information
Figure 6.8
Periods of plasmon beat constituted by different SPP modes
(
m
=
0, 1, 2, and 3) as a function of the Ag wire radius. The permittivity
of the surrounding medium is
D
ε
=
2.25.
sensing. The degree of circular polarization of the emitted photons
fromtheoutputendcanbetunedbythepolarizationangleofthe
incident light. Then, the excitation rate of a chiral object, such as
a chiral molecule, can be controlled by adjusting the local optical
chirality. For this application, the
m
=
0 mode usually serves as a
backgroundexcitationandshouldbeeliminated.Forexample,using
shorter excitation wavelength or changing the incident direction
may facilitate the excitation of the
m
=
1 mode while suppress the
m
=
0 mode (see the discussions following Fig. 6.5). The emission
of SPPs at the output end of the nanowire can be modulated by
the helical pattern, thanks to the coherent interference nature of
chiral SPPs. A rainbow effect, that is, an angle-dependent emission,
is expected. This requires further experimental confirms. With
the above-mentioned properties, a metallic nanowire can serve as
a subwavelength light source that connects many fancy physical
phenomena.
Another attractive application of the chiral SPPs is to use their
helicallydistributedlocalfieldforsubwavelengthplasmoniccircuits.
Successful examples of positive plasmonic devices, such as splitters,
demultiplexers, and modulators [32, 33], have been demonstrated
